Module not found: Can't resolve 'bootstrap/dist/css/bootstrap.min.css' in

I think I have an obscure "where to put things’ #newbie question: in this package

it says “Import Bootstrap CSS in the src/index.js file:” import ‘bootstrap/dist/css/bootstrap.min.css’; …

but when I do this I’m getting

Module not found: Can't resolve 'bootstrap/dist/css/bootstrap.min.css' in '/Users/jason/Work/[XXX]/[xxx].com-front/client/src'

even though I downloaded boostrap 4 and put the CSS files into this location — /client/src/bootstrap/dist/css/bootstrap.min.css

did a miss a step? I don’t understand why bootstrap.min.css is referenced but not explicitly added to the project in the setup instructions.

my App.js file looks like

import React, { Component } from 'react';
import './App.css';
import 'bootstrap/dist/css/bootstrap.min.css';

import { Button } from 'reactstrap';

class App extends Component {
  state = {cities: []}
  async componentDidMount() {
    const response = await fetch('/cities')
    const cities   = await response.json()
    this.setState({cities: cities})
  }
  render() {
    return (
      <div>
        <header>

        </header>
        <Button color="danger">Danger!</Button>
        <ul>
        {this.state.cities.map( city => {
            return <li key={city.name}> <b>{city.name}</b>: {city.population}</li>
          })}
        </ul>
      </div>
  );
  }
}
export default App;